The modern age has shortened the useful life of books and other papers by two principal sources of degradation: The use of acidic paper of wood pulp origins to print the pages of inexpensive or medium-priced books, and the deleterious effect of air pollution, especially in urban areas where most of the reading public is now concentrated. There exist numerous methods of chemical deacidification of books and other papers, but most of them are either costly or require great skill in their safe application; some of these methods need repeated application.
Preservation of books and other papers by storing them at low temperatures and reduced humidity greatly extends their useful life. However, this method has not been widely used because this type of storage stiffens the paper by substantially reducing its internal moisture content. When such a book or other paper is ordered by a reader, there is an unacceptable waiting period of several days or even weeks between the removal of the book from storage and its safe handling by the reader without inflicting permanent damage to the book pages by permanent creases and potential paper breakage along the crease lines.
The present invention reduces this waiting period to an acceptable period of a few hours by placing the book into a vacuum chamber where it is subjected to a partial vacuum and is simultaneously exposed to enough water vapor to restore the flexibility of the book pages. This procedure simultaneously increases the moisture content and raises the temperature of the paper to normal values.
Book storage at low temperatures retards the pace of the chemical reactions which cause the degradation of paper, but in order to be fully effective in its preservative effect, must be accompanied by lowering the humidity inside the storage chamber, with a resulting decrease in the moisture content of the book pages. The resulting loss of flexibility of the book pages temporarily deprives the book of its usefulness, namely its capability of being read without permanent damage to its pages, until the book regains its pre-storage temperature and moisture content. The use of a partial vacuum and water vapor on a book or other paper being retrieved from low-temperature low-humidity storage in accordance with the present invention provides the library with an effective system of preservation storage while satisfying the reasonable demands of the public for efficient book service without an unacceptable waiting period.
In the course of my duties as a paper chemist in the Preservation Office of the Library of Congress (from which position I have now retired), I presented several years ago an article entitled "A Graphical Representation of the Relationship of Environmental Conditions to the Permanence of Hygroscopic Materials and Composites." The article has been published in the Proceedings of Conservation in Archives: International. Symposium, Ottawa, Canada, May 10-12, 1988, printed in Paris: International Council on Archives, 1989. The article recognized and quantified the recognition that storage of books at temperatures and relative humidity well below the human comfort zone greatly extends the useful life of books but also warned that by storage at relative humidities below 20% the paper will become so inflexible as to pose a serious potential for damage in handling.
I made my herein described invention in order to overcome this impediment.
U.S. Pat. No. 5,264,243, Wedinger et al., issued Nov. 23, 1993 to FMC Corporation on an application filed June 16, 1992 discloses a chemical process to deacidify books and other cellulosic materials with certain substituted metal alkoxides applied from a hydrocarbon solution. The foregoing FMC patent also describes, but does not claim, a method of removing the hydrocarbon solvent from the treated books and completing the deacidification reaction by drying the books and repeated applications of a vacuum and water vapor. The FMC patent neither describes nor claims a paper preservation system which includes the use of low-temperature low-humidity storage of books nor does it describe or claim the accelerated restoration of lost flexibility of the book pages upon being removed from storage.